Invertebrates have a complex endocrine system that has developed along with their nervous system. In invertebrates, various endogenous peptides are known that serve as neurotransmitters, neuromodulators or neurohormones.
Mollusks generally have a simpler nervous system as compared to higher animals. Their nervous systems therefore serve as a useful tool in studying the mechanisms of information processing. Any knowledge obtained at cellular level about the information processing mechanisms of mollusks is considered generally applicable to the information processing mechanisms of nervous systems of higher animals For this reason, a significant amount of effort has been made to find neurotransmitters of mollusks.
For example, an endogenous neuropeptide obtained from mussel is disclosed in Japanese Patent Laid-Open Publication No. Hei 1-221392. A novel peptide isolated from ganglia of Achatina fulica is disclosed in Japanese Patent Laid-Open Publication No. Hei 2-286696. This peptide includes a D-amino acid and is found to function as an endogenous neurotransmitter. Japanese Patent Laid-Open Publication No. 6-56890 discloses a neuropeptide isolated from ganglia of a Hungarian snail.
Aside from those described above, various other neuropeptides have been isolated from mollusks and have been identified. Examples include Ala-Pro-Gly-Trp-NH2 (SEQ ID NO: 17), myomodulin-CARP, small cardioactive peptide (SCP), buccalin, and Phe-Met-Arg-Phe-NH2 (SEQ ID NO: 18) (FMRF-amide)(M. Kobayashi and Y. Muneoka, Zool. Sci., 7, 801 (1990); Y. Muneoka and M. Kobayashi, Experimentia 48, 448 (1992); Youjiro. Muneoka, Journal of Pesticide Science 18, 5191 (1993); Y. Muneoka, T. Takahashi, M. Kobayashi, “Perspective in Comparative Endocrinology”, National Research Council of Canada, 1994, p109; A. Di Cosmo and C. Di Cristo, J. Comp. Neurol., 398, 1-12 (1998)).
Mollusks form one of the largest families of invertebrates. Of different species of mollusks, octopuses belong to a group called Cephalopoda. The animals have highly developed brains and far more advanced motor and sensory functions than other members of mollusks. The neurosecretory system of octopuses has been extensively studied. In 1956, Boycott and Young discovered that cutting the optic tract of the animal results in enlarged optic glands and development of gonads. Later, the Wells showed that the gland secretes a gonadotropic hormone (M. J. Wells and J. Wells, J. Exp. Biol., 36, 1-33 (1959)). It turned out that the hormone is a protein hormone and affects the growth of germ cells, the maturation of gonad-related organs, and the synthesis of yolk protein. The hormone is also involved in parenting behaviors of octopuses after their laying eggs (Atlas of endocrine organs, Japan Society for Comparative Endocrinology. ed., Kodansha).
Gonadotropin-releasing hormone (GnRH) was first isolated in 1971 by Schally et al., from the porcine hypothalamus and was then discovered as luteinizing hormone-releasing hormone (LHRH). Its structure was also determined. Since then GnRHs have been studied by many researchers. To date, many GnRHs have been found in different vertebrates such as mammals, birds, and salmon. Also, some suggest that many invertebrates include tissues and substances that are immunoreactive to GnRH (A. Di Cosmo and C. Di Cristo, J. Comp. Neurol., 398, 1-12 (1998)).
It has been shown that, in mammals, GnRHs are secreted from hypothalamus and act on the pituitary gland to cause the release of gonadotropic hormones. These GnRHs are each a decapeptide.
In octopuses, however, the structure of the gonadotropic hormone has yet to be determined although it is known, as described above, that the gonadotropins are secreted from their optic glands. Moreover, no GnRH has yet been isolated from octopuses, nor has its structure been determined.
Accordingly, it is an objective of the present invention to identify, and determine the structure of, a novel GnRH of octopuses. It is another objective of the present invention to understand the activities of the GnRH, the structure of which is determined according to the present invention, both in octopuses and in other invertebrates and vertebrates.
A further objective of the present invention is to provide a novel peptide that can serve as a useful reagent in studying correlations between the structure and the activities of GnRH and in studying the information processing mechanisms of nervous systems in higher animals. A still further objective of the present invention is to provide a novel peptide that can be used as a base compound in the development of pesticides and drugs.
It is yet another objective of the present invention to identify a precursor polypeptide of the GnRH and a gene encoding the precursor for the purpose of expanding our knowledge about evolution of animals. It is yet another objective of the present invention to provide a method for producing the GnRH.